Comma-separated value ("CSV") format is a common semi-standard
text-based format in which fields are delimited by commas.
Spreadsheets and databases are often able to export data in some
variant of it. The intention is that TOPCAT can read tables in
the version of the format spoken by MS Excel amongst other applications,
though the documentation
on which it was based was not obtained directly from Microsoft.

The rules for data which it understands are as follows:

Each row must have the same number of comma-separated fields.

Whitespace (space or tab) adjacent to a comma is ignored.

Adjacent commas, or a comma at the start or end of a line
(whitespace apart) indicates a null field.

Lines are terminated by any sequence of carriage-return or newline
characters ('\r' or '\n')
(a corollary of this is that blank lines are ignored).

Cells may be enclosed in double quotes; quoted values may contain
linebreaks (or any other character); a double quote character within
a quoted value is represented by two adjacent double quotes.

The first line may be a header line containing column names
rather than a row of data. Exactly the same syntactic rules are
followed for such a row as for data rows.

Note that you can not use a "#" character
(or anything else) to introduce "comment" lines.

This format is not detected automatically - you must specify that
you wish to load a table in csv format.